Cover Picture: From Allenes to Tetracenes: A Synthetic and Structural Study of Silyl‐ and Halo‐Allenes and Their Dimers (Eur. J. Org. Chem. 16/2007)

Abstract

AbstractThe cover picture shows the entrance to the World Heritage Site at Newgrange, a 5000‐year‐old Neolithic passage tomb, situated near Dublin. The background depicts a twofold symmetric spiral engraving on the entrance stone and provides an appropriate motif for the sequential transformation of 9‐(trimethylsilylethynyl)‐9H‐fluoren‐9‐ol, via 3,3‐(biphenyl‐2,2′‐diyl)‐1‐(trimethylsilyl)allene, into a series of sterically crowded head‐to‐tail and tail‐to‐tail silyl‐allene dimers with unusually long carbon–carbon and carbon–silicon bonds. Removal of the silyl substituents culminates in the formation of the bis(alkylidene)cyclobutane shown, whose intrinsic C2 symmetry arises solely from the overlap of fluorenylidene fragments with very large wingspans. Details of this work are described in the article by M. J. McGlinchey et al. on p. 2611 ff.